U.S. patent application number 09/981961 was filed with the patent office on 2003-04-17 for split ring bone screw for a spinal fixation system.
Invention is credited to Doubler, Robert L., Hammill, John E. SR..
Application Number | 20030073996 09/981961 |
Document ID | / |
Family ID | 25528761 |
Filed Date | 2003-04-17 |
United States Patent
Application |
20030073996 |
Kind Code |
A1 |
Doubler, Robert L. ; et
al. |
April 17, 2003 |
Split ring bone screw for a spinal fixation system
Abstract
An adjustable spinal fixation system is composed of a collection
of anchoring assemblies attached, via a variety of connectors, to
spine-stabilizing rods. The anchoring assemblies include a linking
member attached in a ball-and-socket fashion to a bone-engaging
member that is adapted to engage a spinal bone of a patient. The
linking member joins one of the included connectors to an
associated bone-engaging member. The connectors are selectively
attached to one of the stabilizing rods. The anchoring assemblies
each include a support collar and a split retention ring that
cooperate to allow adjustment of the bone-engaging member and
corresponding connector during surgery. When surgery is complete, a
securing nut and locking bolt cooperate with the support collar and
split retention ring to maintain the relative position of the
entire fixation system, preventing unwanted movement between the
system components.
Inventors: |
Doubler, Robert L.; (Ida,
MI) ; Hammill, John E. SR.; (Rossford, OH) |
Correspondence
Address: |
Michael A. Slavin, Esq.
McHale & Slavin, P.A.
4440 PGA Boulevard, Suite 402
Palm Beach Gardens
FL
33410
US
|
Family ID: |
25528761 |
Appl. No.: |
09/981961 |
Filed: |
October 17, 2001 |
Current U.S.
Class: |
606/301 ;
606/278; 606/300 |
Current CPC
Class: |
A61B 17/7041 20130101;
A61B 17/7049 20130101; A61B 17/7035 20130101 |
Class at
Publication: |
606/61 |
International
Class: |
A61B 017/70 |
Claims
What is claimed is:
1. In an anchoring assembly for insertion in skeletal bone, said
anchoring assembly having a linking member having a threaded first
end and a substantially-spherical second end; a bone-engaging
member having a first end adapted to engage said bone and a second
end comprising a retention cavity constructed and arranged to
engage said linking member second end, said retention cavity having
a substantially-spherical exterior surface and a circular open
mouth; the improvement comprising a bracing device in said
retention cavity for selectively maintaining said linking member
second end in a chosen orientation within said retention cavity,
said bracing device in the form of a split retention ring having a
diameter greater than the diameter of said circular open mouth and
adapted to frictionally engage said linking member second end; and
a support collar adapted for placement against said bone-engaging
member second end, said collar having a contoured surface sized and
shaped to adjustably engage said exterior surface of said
bone-engaging member second end; whereby said bracing device
selectively prevents relative motion between said linking member
and said bone-engaging member.
2. In an anchoring assembly of claim 1, wherein said support collar
includes a securing nut mounted on said threaded first end of said
linking member; said split retention ring mounted within an
entrance to said retention cavity, said split retention ring
comprising a main body having a substantially-circular cross
section and a gap, the diameter of said circular cross section
being smaller than the diameter of said linking member spherical
second end, thereby preventing removal of said linking member
second end from within said retention cavity, whereby tightening
said securing nut draws said linking member second end against said
split retention ring reducing said gap, thereby preventing motion
of said linking member with respect to said bone-engaging
member.
3. In an anchoring assembly of claim 2, wherein said retention
cavity has a conical inside wall, said wall narrowing toward said
circular mouth, whereby tightening of said securing nut draws said
linking member second end against said split retention ring forcing
said split retention ring along said narrowing conical inside wall
reducing said gap and applying progressive pressure on said linking
member.
4. In an anchoring assembly of claim 3, wherein said first end of
said bone-engaging member has screw threads to engage said
bone.
5. In an anchoring assembly for use with a spinal fixation system,
said spinal fixation system including at least one spine
stabilizing rod and at least one connector adapted to selectively
engage said at least one stabilizing rod; a linking member having a
threaded first end and a substantially-spherical second end, said
threaded first end being sized to engage said connector; a
bone-engaging member having a first end adapted to engage said bone
and a second end comprising a retention cavity constructed and
arranged to engage said linking member second end, said retention
cavity having a substantially-spherical exterior surface; a locking
means for attaching said linking member second end to said
connector; the improvement comprising a bracing device resiliently
disposed in said retention cavity for selectively maintaining said
linking member second end in a chosen orientation within said
retention cavity, said bracing device in the form of a split
retention ring; whereby said bracing device prevents relative
motion between said anchoring assembly and said connector once said
anchoring assembly and said connector have been arranged in a
spinal-curve-correcting orientation.
6. The anchoring assembly of claim 5, wherein said locking means
includes: a securing nut adapted to engage an exterior of said
linking member threaded first end; and a locking bolt adapted to
engage internal threads located within a bolt cavity longitudinally
disposed within said linking member second end; whereby said
securing nut maintains said linking member second end in place when
said second end extends therethrough, and whereby said locking bolt
prevents unwanted relative motion between said securing nut and
said linking member.
7. The anchoring assembly of claim 6, wherein said split retention
ring is mounted within an entrance to said retention cavity, said
split retention ring comprising a main body having a
substantially-circular cross section and opposed ends defining a
gap, the diameter of said circular cross section being smaller than
the diameter of said linking member spherical second end, whereby
said split retention ring prevents removal of said linking member
second end from within said retention cavity, and whereby
tightening said securing nut draws said linking member second end
against said split retention ring reducing said gap, thereby
preventing motion of said linking member with respect to said
bone-engaging member.
Description
[0001] This application is related to an application, entitled
Split Sleeve Locking Modular Hip, S. N. ______, by the same
inventors, filed on even date herewith.
FIELD OF THE INVENTION
[0002] This invention is directed to spinal implant systems and, in
particular, to a multi-component adjustable implant system capable
of maintaining a desired spacial relationship among the bones of a
patient's spine.
BACKGROUND OF THE INVENTION
[0003] This application provides improvements to the articulating
toggle bolt bone screw disclosed in U.S. Pat. No. 5,628,740, issued
to Mullane on May 13, 1997 and U.S. Pat. No. 6,050,997 issued to
Mullane on Apr. 18, 2000. The contents of those patents are hereby
incorporated by reference.
[0004] For individuals with spinal pathologies, the development of
spinal fixation devices represents a major medical breakthrough.
Surgically implanted fixation systems are commonly used to correct
a variety of back structure problems, including those which occur
as a result of trauma or improper development during growth. These
fixation systems typically include one or more stabilizing rods
aligned in a desired orientation with respect to a patient's spine.
Additionally, anchoring screws are inserted into the patient's
spinal bones, and a series of connectors is used to rigidly link
the rods and anchors.
[0005] A variety of designs exist, with each design addressing
various aspects of the difficulties that arise when one reshapes an
individual's spine to follow a preferred curvature. Unfortunately,
known spinal implant systems often correct one set of problems only
to create new ones.
[0006] Common to spinal implant systems is the necessity for proper
anchoring to the bone so as to provide support for the
aforementioned components. While bone screws are commonly used for
anchoring, they are limited in their positioning due to the design
of component pieces. Numerous patents are directed to component
design in order to accommodate the bone screw, yet few patents are
directed to bone screws that will accommodate existing component
design. In many instances the combination of existing component
design and bone screw design inhibits application to a particular
spinal injury. For example, bone structure of the sacrum is
typically soft, and often osteoporotic in the elderly.
Perpendicular placement of a bone screw therein may not be possible
and placement at an angle thereto may cause undue stress further
affecting adjoining bones. Thus, if a common bone screw is
employed, the component connector will be of special design.
[0007] For this and other reasons, screws located in bone structure
typically use a specially designed clamp to attach to a component
such as an alignment rod. A problem with specially designed clamps
is that bone structure cannot be determined until the patient's
bone is exposed causing the necessity of a large inventory of
various sized clamps to be on hand during surgery, of which the
surgeon must search to find the right combination. Even if a clamp
combination is predicted, insertion of the screw may still require
angular insertion due to muscle or tender nerve locations. The
result is a bone screw which exerts unpredictable forces upon
attachment to component connectors. Further, any movement of muscle
and other tissue increases the difficulty of the operation and can
be a major trauma to a person.
[0008] A conventional bone screw consists of a single shaft with a
coarse thread at one end for threading into the bone and a machine
thread at the other end for coupling to components. Another type of
bone screw has a U-shaped top which acts as a saddle for attachment
to an alignment rod. If the screw is placed incorrectly for any
reason, the rod clamp must be made to accommodate the position.
[0009] A number of patents exist which demonstrate the reliance on
the saddle type screw support and various designs to accommodate
the problem.
[0010] U.S. Pat. No. 5,133,717 sets forth a sacral screw with a
saddle support. Disclosed is the use of an auxiliary angled screw
to provide the necessary support in placing the screw in an angular
position for improved anchoring.
[0011] U.S. Pat. No. 5,129,900 sets forth an attachment screw and
connector member that is adjustably fastened to an alignment rod.
An oblong area provided within each connector member allows minute
displacement of the alignment rod.
[0012] U.S. Pat. No. 4,887,595 discloses a screw that has a first
externally threaded portion for engagement with the bone and a
second externally threaded portion for engagement with a locking
nut. The disclosure illustrates the use of a singular fixed
shaft.
[0013] U.S. Pat. No. 4,946,458 discloses a screw which employs a
spherical portion which is adapted to receive a locking pin so as
to allow one portion of the screw to rotate around the spherical
portion. A problem with the screw is the need for the locking pin
and the inability of the base screw to accommodate a threaded
extension bolt.
[0014] U.S. Pat. No. 5,002,542 discloses a screw clamp wherein two
horizontally disposed sections are adapted to receive the head of a
pedicle screw for use in combination with a hook which holds a
support rod at an adjustable distance.
[0015] U.S. Pat. No. 4,854,304 discloses the use of a screw with a
top portion that is adaptable for use with a specially designed
alignment rod to permit compression as well as distraction.
[0016] U.S. Pat. No. 4,887,596 discloses a pedicle screw for use in
coupling an alignment rod to the spine wherein the screw includes a
clamp permitting adjustment of the angle between the alignment rod
and the screw.
[0017] U.S. Pat. No. 4,836,196 discloses a screw with an upper
portion design for threadingly engaging a semi-spherical cup for
use with a specially designed alignment rod. The alignment rod
having spaced apart covertures for receipt of a spherical disc
allowing a support rod to be placed at angular positions.
[0018] U.S. Pat. No. 5,800,435 sets forth a modular spinal plate
assembly for use with polyaxial pedicle screw implant devices. The
device includes compressible components that cooperatively lock the
device along included rails.
[0019] U.S. Pat. No. 5,591,166 discloses an orthopedic bone bolt
and bone plate construction including a bone plate member and a
collection of fasteners. At least one of the fasteners allows for
multi-angle mounting configurations. The fasteners also include
threaded portions configured to engage a patient's bone tissue.
[0020] U.S. Pat. No. 5,569,247 discloses a multi-angle fastener
usable for connecting patient bone to other surgical implant
components. The '247 device includes fastening bolts having
spherical, multi-piece heads that allow for adjustment during
installation of the device.
[0021] U.S. Pat. No. 5,716,357 discloses a spinal treatment and
long bone fixation apparatus. The apparatus includes link members
adapted to engage patient vertebrae. The link members may be
attached in a chain-like fashion to connect bones in a non-linear
arrangement. The apparatus also includes at least one
multi-directional attachment member for joining the link members.
This allows the apparatus to be used in forming a spinal implant
fixation system.
[0022] Another type of spinal fixation system includes rigid screws
that engage the posterior region of a patient's spine. The screws
are adapted with rod-engaging free ends to engage a support rod
that has been formed into a desired spine-curvature-correcting
orientation. Clamping members are often used to lock the rod in
place with respect to the screws. Instead of clamping members,
other fixation systems, such as that disclosed in U.S. Pat. No.
5,129,900, employ connectors that join the support rods and
anchoring screws. The connectors eliminate unwanted relative motion
between the rod and the screws, thereby maintaining the patient's
spine in a corrected orientation.
[0023] Unfortunately, although these so-called "rigid screw"
fixation systems can alter the curvature of a patient's spine, they
can also be difficult to install. In this type of system, the
anchoring screws must be secured in a region that is strong/rigid
enough to support the characteristically-large loads typically
transferred from the support rods. As a result, the number of
suitable anchoring locations is limited. Typically, these screws
are anchored into the posterior region of a patient's spinal column
or into pedicle bone. With rigid screw systems, installation
requires bending a support rod into a path that will not only
correct the shape a patient's spine but that will also engage each
of the installed anchoring screws. Achieving a proper fit between
all of the components while contending with the constraints
encountered during surgery is often difficult. In severe cases, a
suitable fit may not be achieved and the surgery will be
unsuccessful.
[0024] Additionally, the nature of the installation process
required for rigid screw fixation systems often subjects the system
components to pre-loading that unduly stresses the interface
between the patient's bone and the employed anchoring screws. With
these designs, as a patient moves about during daily life, the
system components may become separated from the supporting bone.
Corrective surgery to reattach anchoring screws exposes an
already-weakened region to additional trauma and presents the risk
of additional damage.
[0025] Other spinal fixation systems employ adjustable components.
For example, U.S. Pat. No. 5,549,608 includes anchoring screws that
have pivoting free ends which attach to discrete rod-engaging
couplers. As a result, the relative position of the anchoring
screws and rods may be adjusted to achieve a proper fit, even after
the screw has been anchored into a patient's spinal bone. This type
of fixation system succeeds in easing the rod-and-screw-linking
process. This adjustment capability allows the screws to
accommodate several rod paths. Unfortunately, some adjustable
fixation systems tolerate only limited amounts of relative
adjustment between components, operating best when loaded in one of
several preferred arrangements. As a result, many prior art
adjustable fixation systems are suitable for only a few
situations.
[0026] Additionally, many adjustable fixation systems are prone to
post-surgery component loosening. As a patient moves about during
day-to-day living, his spine is subjected to a seemingly-endless
amount of dynamic loading. Almost all activity requires some form
of back motion; over time, this cyclic movement tends to work the
components of many adjustable fixation systems loose.
[0027] Some adjustable spinal fixation systems include locking
mechanisms designed for long-term, post-surgery securement of the
system components. Although capable of being locked in place, these
systems are often difficult to secure, requiring an excess of tools
during the installation process. The need for extra tools, such as
those required to shave or crimp key portions of a fixation system,
increasing surgical risk by adding complexity and increasing the
number of required steps. Although locking-component fixation
systems exist, many of them unduly increase the dangers of back
implant surgery to an unacceptable level.
[0028] Hardware-intensive fasteners are disclosed in U.S. Pat. No.
5,549,608, in which anchoring screws are fitted with wrenching
flats that allow an anchoring screw to be attached to a patient's
spinal bone with the flats being trimmed away once the screw is in
place. Clamping nuts are then used to secure the anchoring screws
to included stabilizing rods.
[0029] Additionally, many spinal fixation systems do not permit
component repairs. If, for example, a threaded portion of a
connecting member becomes stripped or cross-threaded, the entire
connector must be slid off of the associated stabilizing rod.
Often, such removal produces an undesirable "domino-effect,"
requiring that several connectors be slid off to allow removal of
the damaged connector. Such requirements add unnecessary difficulty
to an already-complex procedure.
[0030] The bone screws shown and described in U.S. Pat. No.
5,628,740 and U.S. Pat. No. 6,050,997 have a bone screw with a
spherical cavity in the proximal end. A toggle bolt with a
spherical distal end is inserted into the cavity in the bone screw.
A collet is forced into the spherical cavity superior to the
spherical end of the toggle bolt. A support collar or attachment
cap is placed over the toggle bolt and tightened down. This forces
the retention collet to engage the spherical portion of the toggle
bolt and the inside of the spherical cavity locking the toggle bolt
in a selected angular disposition. This system requires extremely
accurate machining of the threaded components to result in an
optimum frictional fit. Further, because the collet is a ring, with
a fixed inner diameter, there is only one correct size for the
spherical components. Finally, any deformation of the ring will
lessen the overall frictional contact by creating wrinkles or
ridges on the collet.
[0031] U.S. Pat. No. 5,876,459 to Powell teaches the use of a
deformable collet to form a friction lock between components of an
artificial hip. The collet is expanded outwardly to frictionally
fix an artificial trochanter onto the neck of a ball joint.
[0032] U.S. Pat. No. 4,419,026 to Leto discloses a split ring
camming internal locking device used with telescoping tubular
members for transporting liquids. The ring is split for flexing to
fit around the internal tube and for resiliently sealing against
the external tube.
[0033] Thus, what is needed is a spinal fixation system that
includes the advantages of known devices, while addressing the
shortcomings they exhibit. The system should allow component
adjustment during installation, thereby enabling satisfactory
correction of a wide variety of spinal deformities. The system
should also include a component locking mechanism that is simple
and reliable. The system should include two-piece connectors that
may be mounted along a support rod, in-between previously-secured
connectors. The system should also include mounting hardware that
secures with a minimum of tools and that allows modular replacement
of components damaged during installation.
SUMMARY OF THE INVENTION
[0034] The present invention is a bone screw for use in a spinal
fixation system for reshaping the spine of a patient. The bone
screw has threads on one end for anchoring in the spine. The other
end has a spherical connector with a conical cavity therein. The
cavity has the larger diameter base of the cone toward the threaded
end of the screw and a narrower mouth. The mouth of the conical
cavity accepts the spherical end of a toggle bolt such that the
toggle bolt and the bone screw are connected by a ball joint. To
prevent disassembly of the bone screw and toggle bolt, an
associated split retention ring locking mechanism is inserted in
the conical cavity between the spherical end of the toggle bolt and
the mouth of the cavity. The resilient split retention ring can be
compressed to reduce it's diameter for insertion through the mouth
of the cavity and then expands to fill the conical cavity superior
to the spherical end of the toggle bolt.
[0035] Because of the flexibility and resilience of the split
retention ring, the mating parts do not require fine tolerances and
are less expensive to make. Further, the split retention ring
provides infinite adjustment of the locking pressure as the toggle
bolt is tightened into the assembly. The system is modular,
employing a collection of anchoring assemblies that are linked, via
various connectors, to strategically-arranged stabilizing rods. The
stabilizing rods are shaped and aligned to impart a preferred
curvature to a patient's spine.
[0036] The anchoring assemblies are multi-piece units characterized
by linking members that are joined in a ball-and-socket-type
arrangement with a corresponding bone-engaging member. During use,
the bone-engaging member is secured to a spinal bone and the
linking member is secured to one of the stabilizing rods via a
corresponding connector. The bone-engaging member may include
coarse, external threads or have a hook-shaped end. Each anchoring
assembly also includes a support collar that provides a secure
interface between the bone-engaging member and associated
connector. Each anchoring assembly also includes a securing nut and
a locking bolt that cooperate to prevent unwanted,
post-installation motion within the anchoring assembly. The
securing nut and locking bolt also prevent unwanted relative motion
between the anchoring assembly and associated connector.
[0037] The connectors are rigid structures adapted to link an
associated anchoring assembly with one of the stabilizing rods. In
one embodiment, the connectors are two-piece constructions that
allow the connector to engage a stabilizing rod in a sandwich-type
arrangement, permitting connector installation and removal that
does not disturb adjacent connectors.
[0038] The stabilizing rods are rigid members shaped to form a
spine-curvature-correcting path. Attaching each anchoring assembly,
via connectors, to a stabilizing rod forces a patient's back into a
surgeon-chosen shape. Stabilizing rods may be used singly, or in
pairs, depending upon the type of correction required. The rods
vary in size, but typically extend between at least two
vertebrae.
[0039] Thus, it is an objective of the present invention to provide
a bone screw assembly for a spinal fixation system that permits
component adjustment during installation, thereby enabling
satisfactory correction of a wide variety of spinal
deformities.
[0040] It is an additional objective of the present invention to
provide a bone screw assembly that includes a split ring locking
mechanism that is simple and reliable.
[0041] It is a further objective of the present invention to
provide a spinal fixation system that includes two-piece connectors
that may be mounted along, and removed from, a support rod without
requiring movement of adjacent connectors.
[0042] It is yet another objective of the present invention to
provide a spinal fixation system that includes mounting hardware
which requires a minimum number of tools.
[0043] It is also an objective of the present invention to provide
a spinal fixation system that allows modular replacement of damaged
components.
[0044] Other objects and advantages of this invention will become
apparent from the following description taken in conjunction with
the accompanying drawings wherein are set forth, by way of
illustration and example, certain embodiments of this invention.
The drawings constitute a part of this specification and include
exemplary embodiments of the present invention and illustrate
various objects and features thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] FIG. 1 is a pictorial view of the spinal fixation system of
the present invention;
[0046] FIG. 2 is a perspective view of an anchoring assembly used
in the present spinal fixation system;
[0047] FIG. 3 is a perspective view of an anchoring assembly used
in the present spinal fixation system, having a support collar
removed;
[0048] FIG. 3A is a perspective view of a support collar used in
the present spinal fixation system;
[0049] FIG. 4 is a pictorial view of a bone-engaging member from an
anchoring assembly of the present invention;
[0050] FIG. 4A is a pictorial view of a linking member from an
anchoring assembly of the present invention;
[0051] FIG. 4B is a pictorial view of a split retention ring of the
present invention;
[0052] FIG. 5 is a pictorial view of an alternate embodiment of an
anchoring assembly and connector of the present invention;
[0053] FIG. 6 is a close-up view of an alternate embodiment of a
split retention ring of the present invention; and
[0054] FIG. 7 is a close-up view of the alternate anchoring
assembly and connector shown in FIG. 5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0055] It is to be understood that while a certain form of the
invention is illustrated, it is not to be limited to the specific
form or arrangement of parts herein described and shown. It will be
apparent to those skilled in the art that various changes may be
made without departing from the scope of the invention and the
invention is not to be considered limited to what is shown in the
drawings and described in the specification.
[0056] Now with reference to FIG. 1, the spinal fixation system 10
of the present invention is shown. By way of overview, the Fixation
System 10 includes a collection of bone-engaging anchoring
assemblies 12 that are joined via connectors 14, 14' to stabilizing
rods 16, 16'. The specifics of the spinal fixation system 10 will
now be discussed in more detail.
[0057] With additional reference to FIG. 2, one of the included
anchoring assemblies 12 is shown in an assembled state. FIGS. 3 and
3A show the anchoring assembly with an associated support collar 18
removed. In addition to the support collar 18, each anchoring
assembly 12 also includes a pedicle screw 20, a toggle bolt 22, and
a split retention ring 24. As shown in FIG. 4, each pedicle screw
20 also includes a ball end 28 spaced apart from the threaded end
26 by a neck portion 30. The exterior 32 of the pedicle screw ball
end 28 is preferably contoured for easy grasping. The interior of
the pedicle screw ball end 28 forms a retention cavity 34,
discussed below. The entrance 36 to the retention cavity 34 is
characterized by a securing lip 38 that extends radially into the
retention cavity 34.
[0058] Each toggle bolt 22, as shown in FIG. 4A, includes a ball
end 40 and an opposite threaded end 42. As seen in FIG. 3, the ball
end 40 of the toggle bolt 22 is shaped and sized to fit inside the
pedicle screw retention cavity 34. Preferably, the interior of the
retention cavity is substantially conical but slightly larger
dimensions than the spherical contours of the toggle bolt ball end
40.
[0059] With reference to FIG. 4B, the split retention ring 24
includes a gap 44 separating the opposite ends of the split
retention ring main body 46. As seen in FIG. 3, the split retention
ring 24 is used as a bracing means to secure the ball end 40 of the
toggle bolt 22 within the pedicle screw retention cavity 34. More
specifically, after the toggle bolt ball end 40 is placed within
the pedicle screw retention cavity 34, the split retention ring 24
is pushed through the entrance 36 of the retention cavity 34 by
reducing the gap 44 facilitating travel past the engagement lip 38,
thereby bringing the split retention ring main body 46 to rest
against the engagement lip by spring action resilience of the split
retention ring 24.
[0060] With this arrangement, the split retention ring 24 allows
pivotal movement of the toggle bolt 22 within the retention cavity
34, while preventing removal of the toggle bolt therefrom. Once the
split retention ring 24 and toggle bolt 22 are in place, the
threaded end 42 of the toggle bolt is inserted through a
passthrough aperture 48 of the support collar 18. This is shown in
FIG. 2.
[0061] Once the toggle bolt 22 has been passed through the support
collar passthrough aperture 48, the support collar 18 comes to rest
against the pedicle screw ball end 28. Although several shapes are
possible, the interior of the support collar 18 preferably has a
spherical contour that matches the exterior 32 of the pedicle screw
ball end 28. This arrangement limits the relative motion possible
between the support collar 18 and the toggle bolt 22, while
allowing the toggle bolt ball end 40 to rotate freely within the
pedicle screw retention cavity 34. Although an assembly process has
been described above, the anchoring assemblies 12 are typically
delivered to the end-user surgeon as a finished unit.
[0062] With additional reference to FIG. 3, the threaded interior
bore 122 of the toggle bolt threaded end 42 has a hexagonal cross
section. This allows the insertion of an allen wrench, not shown,
into the interior bore 122 to prevent relative motion between the
spherical ball end 40 of the toggle bolts 22 and the conical
retention cavity 34 of the pedicle screw 20. The inserted allen
wrench thereby prevents unwanted spinning of the toggle bolt 22
within the retention cavity 34 while the securing nut 116 is
tightened onto the exterior threads 120.
[0063] Tightening the securing nut 116 forces the toggle bolt
threaded end 42 to travel longitudinally through the passthrough
aperture 84 and also causes the toggle bolt ball end 40 to be
forced against the split retention ring 24 reducing the gap 44.
Further tightening of the securing nut 116 forms a substantially
rigid fit between the toggle bolt 22 and the pedicle screw 20. With
the securing nut 116 tightened appropriately, the toggle bolt
threaded end 42 is locked in place with regard to the right-facing
straight connector attachment flange 82, and the toggle bolt ball
end 40 is locked in place within the pedicle screw retention cavity
34. In this state, the split retention ring is sandwiched between
the exterior of the toggle bolt ball end 40 and the conical
interior of the retention cavity 34. Since the split retention ring
24 is locked within the retention cavity 34 by the retention cavity
engagement lip 38, relative motion between the toggle bolt ball end
and the pedicle screw 20 is prevented once the toggle bolt threaded
end 42 is locked in place by the tightened securing nut 116. This
results in a rigid link between the right-facing straight connector
and the anchoring assembly 12.
[0064] Although the above description refers to joining an
anchoring assembly 12 specifically to a right-facing straight
connector 52, each of the one-piece connectors 14 and two-piece
connectors 14' may be attached to an anchoring assembly in a
similar manner. That is, right-facing offset connectors are
attached by inserting a toggle bolt threaded end through the
associated passthrough aperture; left-facing offset connectors are
joined with an anchoring assembly by inserting a toggle bolt
threaded end through an associated passthrough aperture; and
left-facing straight connectors are attached to anchoring
assemblies by inserting a toggle bolt threaded end through an
associated passthrough aperture. In each case, the exterior threads
120 of the inserted toggle bolt threaded end 42 are held in place
by a tightened securing nut 116, as described previously.
[0065] To prevent unwanted loosening of a connector 14, 14' and
anchoring assembly 12 union, a locking bolt 118 is inserted into
the threaded interior bore 122 of the toggle bolt corresponding to
each anchoring assembly that has been secured in place. As
mentioned above, each locking bolt 118 has a left-handed thread
pattern, thereby matching the left-handed thread pattern of each
toggle bolt threaded interior bore 122. The locking bolt 118 is
screwed into an associated toggle bolt threaded interior bore 122
until the locking bolt head plate comes to rest against the
securing nut 116 that holds the corresponding anchoring assembly 12
in place with respect to the associated connector 14, 14'.
Incorporating this locking bolt 118 ensures that anchoring
assemblies 12 and connectors 14, 14' stay locked in place, thereby
preventing unwanted relative motion within the spinal fixation
system 10.
[0066] Now with reference to FIG. 5, an alternate embodiment of an
anchoring assembly 12' is shown secured to a right-facing straight
connector 52. In this embodiment, a alternate split retention ring
24' is used to secure the toggle bolt ball end 40 within a securing
cavity 34' disposed within the ball end 28 of an associated pedicle
screw 20'. The securing cavity 34' has a conical wall 45 tapering
from a wider base toward a narrower mouth. Relative position
between the pedicle screw 20 and the connector 52 is maintained by
an associated support collar 18. The support collar 18 is disposed
between the pedicle screw ball end 28' and the attachment flange 82
of the connector 52.
[0067] With reference to FIG. 6, a close-up view of an alternate
embodiment of the split retention ring 24' is shown. The exterior
surface of the ring 24' is characterized by conical shaped wall 46'
and a gap 44'. With additional reference to FIG. 7, the conical
wall of the split retention ring 24' is complimentary to the
conical wall of retention cavity 34. Additionally, interior surface
of the conical split retention ring 24' has a smaller diameter
circular shoulder 47 shaped and sized to engage the exterior
surface of an associated toggle bolt ball end 40.
[0068] The spinal fixation system 10 is preferably formed from
rigid, biocompatible materials. One such preferred material is
titanium; however, other materials may be used as well.
[0069] Although the invention has been described in terms of a
specific embodiment, it will be readily apparent to those skilled
in this art that various modifications, rearrangements and
substitutions can be made without departing from the spirit of the
invention. The scope of the invention is defined by the claims
appended hereto.
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